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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Is CO2 a pollutant?

What the science says...

Although it has some very important and beneficial effects, CO2 meets the legal and encyclopedic definitions of a "pollutant", and human CO2 emissions pose a threat to public health and welfare.

Climate Myth...

CO2 is not a pollutant
'To suddenly label CO2 as a "pollutant" is a disservice to a gas that has played an enormous role in the development and sustainability of all life on this wonderful Earth. Mother Earth has clearly ruled that CO2 is not a pollutant.' (Robert Balling, as quoted by Popular Technology)

Before assessing whether or not CO2 is a pollutant, we must first define the term.

What is an Air Pollutant?

The US Clean Air Act was incorporated into the United States Code of Federal Regulations, Title 42, Chapter 85. Its Title III, Section 7602(g) defines an air pollutant:

The term “air pollutant” means any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive (including source material, special nuclear material, and byproduct material) substance or matter which is emitted into or otherwise enters the ambient air.

Clearly this is a very broad definition. More importantly, its Title 42, Section 7408 states that the US Environmental Protection Agency (EPA) Administrator must publish a list of certain air pollutants:

"emissions of which, in his judgment, cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare"

"greenhouse gases in the atmosphere may reasonably be anticipated both to endanger public health and to endanger public welfare....The major assessments by the U.S. Global Climate Research Program (USGCRP), the Intergovernmental Panel on Climate Change (IPCC), and the National Research Council (NRC) serve as the primary scientific basis supporting the Administrator’s endangerment finding."

Greenhouse gases including CO2 unquestionably fit the Clean Air Act's broad definition of "air pollutants," and must be listed and regulated by the EPA if it can be determined that they endanger public heath and/or welfare.

"the addition of any substance (solid, liquid, or gas) or any form of energy (such as heat, sound, or radioactivity) to the environment at a rate faster than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form."

Thus legally in the USA, CO2 is an air pollutant which must be regulated if it may endanger publich health or welfare. And according to the encyclopedic definition, CO2 is a pollutant unless our emissions can be stored "harmlessly."

Is Increasing CO2 Dangerous or Harmless?

Humans are Increasing Atmospheric CO2 Concentrations

Humans have increased the amount of CO2 in the atmosphere by 40% over the past 150 years, primarily through the combustion of fossil fuels.

Figure 1: CO2 levels (parts per million) over the past 10,000 years. Blue line from Taylor Dome ice cores (NOAA). Green line from Law Dome ice core (CDIAC). Red line from direct measurements at Mauna Loa, Hawaii (NOAA).

We know that the increase in atmospheric CO2 is anthropogenic from a number of lines of evidence. Atmospheric oxygen is decreasing at approximately the same rate as the atmospheric CO2 increase, which tells us that the source of the change is from a release of carbon combining with atmospheric oxygen rather than a natural release of CO2. We also know that the 30 billion tonnes of CO2 released by human activity must go somewhere, and in fact atmospheric CO2 is only increasing by about 16 billion tonnes per year (the rest is going into the oceans). CO2 produced from burning fossil fuels or burning forests also has quite a different isotopic composition from CO2 in the atmosphere, because plants have a preference for the lighter isotopes (12C vs. 13C); thus they have lower 13C/12C ratios. And indeed we've observed this ratio decline in the atmosphere.

The Increasing CO2 is Causing Global Warming

Thus we know that human emissions are increasing the amount of CO2 in the atmosphere, which as a greenhouse gas, in turn increases the greenhouse effect. This increases the amount of energy (in the form of longwave infrared radiation) reaching the Earth's surface. We've observed this increase through spectroscopy, which measures changes in the electromagnetic spectrum. Climate scientists have also quantified the amount of warming we expect to see from the energy imbalance caused by this increased downward radiation, and it matches well with observations. Given the amount of CO2 humans have added to the atmosphere already, once the planet reaches a new equilibrium state, it will have warmed approximately 1.4°C from pre-industrial levels. Additionally, we have observed numerous key 'fingerprints' of anthropogenic global warming which confirm that the warming we've experienced is due to an increased greenhouse effect.

Quantifying exactly at what point global warming will become dangerous is a difficult task. However, based on the research and recommendations of climate scientists, more than 100 countries have adopted a global warming limit of 2°C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts, and damages. This 2°C warming level is considered the "danger limit". During the last interglacial period when the average global temperature was approximately 2°C hotter than today, sea levels were 6.6 to 9.4 meters higher than current sea levels. Large parts of the Antarctic and Greenland ice sheets melted, with the southern part of Greenland having little or no ice.

As discussed above, the CO2 we've already emitted has committed us to about 1.4°C warming above pre-industrial levels. Given a climate sensitivity to a doubling of atmospheric CO2 of 2-4.5°C and the fact that on our current path we're headed for a CO2 doubling by mid-to-late 21st century, we're fast-approaching the danger limit.

How Soon Will we Reach Dangerous Warming?

Meinshausen et al. (2009) found that if we limit cumulative CO2 emissions from 2000-2050 to 1,000 Gt (approximately an 80% cut in global emissions), there is a 25% probability of warming exceeding the 2°C limit, and 1,440 Gt CO2 over that period (an 80% cut in developed country emissions) yields a 50% chance of 2°C warming by the year 2100. If we maintain current emissions levels, there is an approximately 67% chance that we will exceed 2°C warming by 2100.

Figure 3: Probability of exceeding 2°C warming by 2100 in various emissions scenarios in gigatonnes of carbon (RealClimate)

In short, to avoid the amount of global warming which is considered dangerous based on our understanding of the climate and empirical evidence, we need to achieve major reductions in global CO2 emissions in the next 40 years. Thus it becomes quite clear that not only is CO2 a pollutant, but it also poses a risk to public health and welfare.

Ocean Acidification

Another impact of increasing atmospheric CO2 emissions is ocean acidification. When CO2 dissolves in seawater, it increases the hydrogen ion concentration though the chemical reaction CO2 + CO32- + H2O → 2HCO3-, thus decreasing the pH of the oceans (NOAA 2008). Among other impacts, this decreasing oceanic pH has a damaging effect on corals, which form the habitat of approximately 25% of marine species (Karleskint et al. 2009). A seminal study co-authored by 17 marine scientists (Hoegh-Guldberg et al. 2007) found:

"Many experimental studies have shown that a doubling of pre-industrial [CO2]atm to 560 ppm decreases coral calcification and growth by up to 40% through the inhibition of aragonite formation (the principal crystalline form of calcium carbonate deposited in coral skeletons) as carbonate-ion concentrations decrease"

Thus not only does anthropogenic CO2 act as a dangerous pollutant due to its impacts on global warming and climate change, but it also has a major effect on marine ecosystems through ocean acidification.

CO2 is a Pollutant

When considering the legal definition of "air pollutants" and body of scientific evidence, it becomes clear that CO2 meets the definition and poses a significant threat to public health and welfare.

Further reading

Comments

Plants can't grow any better than their limiting factor, which might be not CO2, but nitrogen, water, light,....

Even if they do grow "better," the betterment often is not to the advantage of farmers; for example, the extra mass can go into non-consumable woody stalk, which makes the crop more expensive to process than any extra grain/fruit value.

And weeds such as poison ivy and kudzu respond much "better" to increased CO2 than do many crops, but "better" is not better for people, and not better for plants that those weeds compete with.

The Duke FACE experiment (Free-Air CO2 Enrichment) of artificially fertilizing trees with CO2 is an important one. Its results are consistent with other experiments on other plants: Plants' growth is limited by whichever nutrient or other condition is in shortest supply or detrimentally high supply, or by inherent physiological limits. A plant whose growth is limited by water supply isn't going to grow more if you give it more CO2, or more sunlight, or more soil nutrients. If initially the CO2 supply is the limiting factor, then giving the plant CO2 will let it grow faster only until some other factor that was sufficient for the previous growth rate becomes the bottleneck for the higher growth rate. Farmers and gardeners know this, which is why they don't waste money by giving plants too much of any one thing. Even greenhouses whose air is spiked with CO2 don't have 100% CO2 atmospheres.

"Detrimental conditions" include temperatures that are too high. Even if a plant has sufficient other nutrients and conditions to allow it to take advantage of extra CO2 to grow more, if that CO2 is accompanied by higher temperature, the temperature can slow growth. The net growth then will depend on the balance of the enhancement from CO2 and the detriment from temperature.

But even if you keep all the nutrients and conditions in synch, there are inherent physiologic limits to growth rate. All plants in the world today have evolved for, or been bred for, approximately the current CO2 levels. There was no survival advantage of being able to use more CO2 than was available.

"Forests will continue to be important to soak up anthropogenic carbon dioxide," says [the aspen FACE experiment's] Waller. "But we can't conclude that aspen forests are going to soak up excess carbon dioxide. This is going to plateau."

"Aspens are already doing their best to mitigate our inputs," agrees Cole. "The existing trees are going to max out in a couple of decades."

Based on available evidence from the Duke experiment, “I’d be surprised if the forests of the world will take up more than one-third of the carbon dioxide from fossil fuel emissions in the year 2050, which is what our experiment simulates,” he predicted.

More information on biologic carbon sequestration, with a number of links to even more info, can be found on an EPA page. Wikipedia has a broader page.

These references seem to suggest those 'limiting factors' to potential sequestration are significant and supportive of your quotes under 'the bottom line'.

From an older issue of Nature:"Doubts concerning the potential of natural vegetation for sustained response to rising CO2 have arisen from experiments on infertile soils, where the stimulus to growth was curtailed by mineral nutrient limitations. Here we present evidence that mineral nutrient constraints on the fertilizer effect of elevated carbon dioxide can also occur on fertile soil "

Also from Nature:"Soil carbon was lost at subambient Ca, but was unchanged at elevated Ca where losses of old soil carbon offset increases in new carbon. ... differences in sensitivity of carbon storage to historical and future Ca and increased nutrient limitation suggest that the passive sequestration of carbon in soils may have been important historically, but the ability of soils to continue as sinks is limited."

From Frontiers in Ecology and the Environment:"research suggests that the fertilization effect is limited by nutrients and air pollution, in addition to the well documented limitations posed by temperature and precipitation. This review suggests that existing forests are not likely to increase sequestration as atmospheric CO2 increases."

Apologies to the Moderator. I posted in the wrong place as a result of not properly familiarising myself with the layout,prior to posting.
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AWoL at 07:28 AM on 29 June, 2010
I'm just a vet, though believe it or not, I can remember Boltzman's Constant from our old Physics lectures, so I like to believe that I inhabit the ranks of the scientific semi-literate.

My question is, if the Earth has an arbitrary average temperature of circa 15degC and the temperature of space is 270degK ie -270degC, then what's the problem? Anything that stems the ferocious heat loss to the exterior, surely has to be a good thing? Surely the correct thing to do is to pump CO2( or more potent greenhouse gases) into the atmosphere in order to keep the planet as warm as possible?
What a nutty idea , I hear you say, but in reply I say....-270degC, out there. Not much chance of too much warming when you're up against that. It's bloody cold out there!
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scaddenp at 08:14 AM on 29 June, 2010
Awol - "as warm as possible". Why not even more potent GHGs then and get us to Venus-like temperatures? Well obviously because we want planet to be around the temperatures we evolved to live in. However, this debate isnt really about what would be an optimal temperature but is about how fast we are changing it. Think of your farm animals and about how easily farmers are able to cope with rapid climate change. We have huge urban centers and complex food production systems that have developed in stable climate. Rapid change is not good for them. Ask how farmers on the great deltas are going to cope with coast erosion and salt incursion as sealevel rises as well. Over a 1000 years (ice cycle type change) possible. Over 100 years - hmm.

AWoL replies
scaddenp has given an answer of sorts,but I have to say I'm not entirely satisfied.
The Venus comparison is no good as there is a lot of controversy over the workings of the Venusian atmosphere.Most agree that it is not comparable to Earth, and in fact the greenhouse effect of CO2 plays but a small part in explaining the high surface and atmospheric temperatures on that planet.

Regarding the consequences of the overheated planet which you envision. Why all the doom and gloom? In the deltas that you mention, could not the farmland, assumimng that there is any, be replaced with fish-farming and shellfish production? People could live on man-made islands as have been constructed in Dubai.In Japan and Hong kong hasn't there been considerable land reclamation? Then there's the Dutch and their dykes.Isn't nature herself lending a hand in the creation of new land ie the Surtseys and the Icelandic Westmann Islands. Isn't isostatic rebound still underway from the last ice age? Or has that come to a stop?
With regard to agricultural production, I can't help feel that you are miles off the beam. Wasn't it Herschel the astronomer, that correlated increased sunspot activity with lower grain prices? Everything starts from plants. What's good for plants is good for animals which is good for people.Plants like the heat,given adequate water, and they positively love CO2.

Where you, scaddenp,see doom and disaster, I see formerly barren territories transformed into luxuriant swards and dense woodlands, inhabited by contented happy people.
That's the bit I don't get. Why is climate change, ie getting hotter, always accompanied by doom and disaster when if anything it is more likely to be accompanied by happiness and prosperity? Any changes are not going to happen overnight, so there's plenty of time to react.And never before have people been able to move so rapidly, and easily establish new settlements, thanks to the extra power to their elbow of readily combustible,energy-dense hydrocarbons.Markets and the intiative of adaptable people will solve any problems far more effectively than any number of governmental organisations.

The Sahara was once green. There was no UN in those days.The people didn't die, but moved, adapted and went forth and multiplied......and very good at multiplication they were ..... a bit too good, for their own good, I sometimes think.

Quite a bit of unsupported speculation there, AWoL. Other people with skills specific to the various spheres of knowledge you touch upon draw different conclusions.

Anyway, with regard to unchecked formerly insignificant pollutants emerging from burgeoning cultural intensity we have lessons from the past to draw upon. Government (us, acting in concert) ends up owning solutions nobody else can or will provide.

For a specific example of effective solutions to pressing need arising from inadvertent effects of commercial activity in combination with exploding demand see the example of cholera and typhoid emerging in London and other developing urban systems. A key feature of this story is that established commercial forces nearly invariably resisted attempts to solve the fundamental causes of these diseases, leaving the public in the form of government eventually forced to insist by agreed-on coercion.

AWoL, regarding the benefits of CO2 itself for plants, see the comments before yours on this thread. Click on the links within those comments for supportive details.

Regarding your other contentions, see the broader post It’s not bad, which lists positives versus negatives of not just more CO2 for plants to consume, but of all the effects of higher CO2 levels, including warming and ocean acidification.

This post is a continuation of a discussion at the thread "Watts it like at a climate skeptic speakers event?" in response to
post 104, Marcus at 09:41 AM on 23 June, 2010.
The Marcus post remains at that thread whilst my reply was selectively deleted. I have copied the Marcus post here to provide some continuity, it follows after my response.

My response:-
The most obvious point being overlooked is that the limitations listed are not new, nature has RARELY provided ideal conditions, some would swear never.
The less than ideal conditions have been there ever since agriculture was first developed, especially, ESPECIALLY, in Australia in the regions similar to where the Horsham FACE trial was conducted which not only simulated higher CO2 levels, but HOTTER and DRIER conditions as well. So far 3 trials have been done over 3 years, 3 below average years, and are ongoing.

A couple of points :-
(1)Seed yield increased significantly whilst seed protein fell slightly EXACTLY as has always has happened under natural conditions. Nothing new there.
(2)Protein yield per hectare INCREASED meaning the process of producing more food from less land can continue.
(3)Increased non-grain biomass assists in improving soil carbon content. To increase soil carbon content by 1 tonne per hectare, an extra 4.4 tonnes of dry matter per hectare has to be returned to the soil.
(4) Irrespective of CO2 levels, higher outputs require higher inputs of water and nutrients. ALWAYS HAS.
However indications are that under higher CO2 levels, water utilisation efficiency is INCREASED.

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Marcus at 09:41 AM on 23 June, 2010
Sorry moderator, but I just can't let John D's latest comments go by without a response.

You seriously don't get it-do you John? Nobody here has claimed that-under ideal conditions-CO2 *can't* be a plant food. What they've claimed is that its not that simple because (a) global warming won't provide for ideal conditions & (b) that it is nitrogen, water & trace elements that are more limiting factors on plant growth than CO2 abundance.
For all your talk, you've not managed to answer several key questions which are:

(a) under ideal conditions, can increased CO2 levels enhance plant biomass for the long-term, given acclimation?

(e) will increased CO2 levels impose any additional costs on farmers? (very important given the slim margins on which most farmers operate).

Based on the evidence provided by the *one* FACE trial you've linked to, I'd say the answer is that, (a) though increased CO2 can provide short-term increases in total biomass (under ideal conditions) acclimation might eventually erode those benefits; (b) that though there was a significant increase in total plant biomass, this wasn't translating into significant increases in seed yield for most varieties & (c) that seed quality (in terms of protein content) was decreased, but total nitrogen demand from the plant was increased. As someone who actually deals with farmers on a regular basis, if you were to try & promote that to farmers as a *benefit* from increasing CO2 emissions, they'd probably laugh in your face-rightly pointing out that ideal conditions are already hard to come by, that seed yield & seed quality are all that's ultimately important, & that they would be ill-equipped to afford the significant increase in fertilizer costs that this enriched CO2 environment would demand.
-----------------------------------

AWOL - lets ignore the completely hilarious non-physical stuff about venus. The point I was making is that you cant live on venus, there IS an upper bound on temperature and if you chose enough of powerful enough GHG, then we turn earth that way too. The MAIN point I was making is that RATE of change is the cause for concern - too fast for ecological systems to cope with. Current rate of change is too fast, let alone the projected future rate of change. Its the rate that is the problem. Your happy scenario might play out over 1000s of years and as for comments on deltas, I assume you dont live on one. This is fantasy stuff. Ask yourself why all the existing drowned deltas are the happy places you imagine and they drowned with sealevel rates much slower than current and projected.

As for CO2 is plant food. Please see other comments in this thread and some reputable science. CO2 does not magically gives the plants extra water or nutrients.

Doug Brostron makes a good point in favour of government with respect to cholera in London. However, when governments get involved in commercial activity they invariably mess up. The Russian cotton industry and the disaster of the Aral sea and the dismal performance of collectivisation. But you're right, and I shall have to add public health to the short list of those things that governments are good at.

Regarding the effect of CO2 on plants and particularly crops. I checked and indeed much of which you say is true, especially in already drought prone marginal areas. However northern latitudes are expected to benefit. At least in the short- term. There could be problems later, if temperatures rise......but only if temperatures rise.Unfortunately throughout most of those articles, the assumption is made that because CO2 is going up and temperature is going up, then the two are inextricably linked.
Whilst there are warnings about a decline in seed quality, growers in Holland are pumping CO2 into greenhouses to obtain increased output in the order of 20-30%. Benefits fall off after 1000ppm and indeed higher levels are harmful. If anyone says, as I have done up to now, that plants can't get enough of the stuff, then that is indeed plain wrong. However I have heard it said, that it will be very difficult to get above 600ppm(atmospheric) even with no brakes applied to hydrocarbon consumption.True or false?
So far I haven't come across any complaints about CO2 enhancement being a waste of time and money.
If world output is going to be affected, water availability and temperature would seem to be bigger factors than CO2 levels. Obviously there are going to be changes, and winners and losers, but overall won't things carry on much as they are?

Scaddenp makes the point about rapidity of change. An example or two, if poss please? Can't say I've noticed very much different here in Britain and the continent. Drought seems to be problem in Australia... but what's unusual about that? And while we're at it, where are the drowned deltas? I thought I was fairly well clued up on Geography, but maybe not. Maybe, when making a statement, you could provide an example or two?

ScienceDaily (May 9, 2003) states that higher levels of CO2 may allow forests to grow in arid areas that once were unsupportive of trees.

This information comes from studies in the Negev, one of the driest places on earth.

"Plants need carbon dioxide for photosynthesis, which leads to the production of sugars. But to obtain it, they must open pores in their leaves and consequently lose large quantities of water to evaporation. The plant must decide which it needs more: water or carbon dioxide. Yakir suggests that the 30 percent increase of atmospheric carbon dioxide since the start of the industrial revolution eases the plant’s dilemma. Under such conditions, the plant doesn’t have to fully open the pores for carbon dioxide to seep in – a relatively small opening is sufficient. Consequently, less water escapes the plant’s pores. This efficient water preservation technique keeps moisture in the ground, allowing forests to grow in areas that previously were too dry."

In fact one proposal suggests that all the world's industrial release of CO2 could be absorbed by planting trees in the deserts of the world and in particular the Sahara. Haaretz Tue, July 27, 2010Israeli ecologists could help stop global warming.

Another reason CO2 can be considered a pollutant is that it cools the stratosphere(cool stratospheric conditions promote ozone destruction), and delays the recovery of the ozone hole. Is it possible that CO2 could actually worsen the ozone hole?

Isn't the thousands of words spent on explanation missing one fundamental point? Whilst everyone is saying higher CO2 is causing higher temperatures, they are missing the point that CO2 cannot be generated without heat and increases in composting. Charts show CO2 peaks after temperatures start dropping so in a sense is not CO2 a stabilizer of temperature.

Talking with a highly respected agronomist the other day about this very thing, explained how much Carbon capture is being forced through agriculture these days. When considering the millions of acres that are agriculture and being given over to this form of farming, then we should be looking in other areas to lay the blame at mans feet.

Such as ozone, the affects of this still have not left us and are on going.

The variation in CO2 that reinforces the ice-age cycle is biogenic - Ocean effects, swamp methane, vegetation change. The CO2 that is causing current warming comes from burning fossil fuels. The biogenic feedbacks that come with increased temperatures are slow and make hardly any contribution yet. How do we know where the CO2 comes from (both in atmosphere today and in the past)? Isotopes of carbon. Fossil and biogenic have different signature.

In his attempts to hijack yet another thread, BP once again assures as of the hackneyed old "CO2 is plant food" meme-even showing us pictures of soybeans grown in otherwise ideal conditions to back him up.

Of course, what he is not aware of is a little thing called "acclimation"-which effectively means that C3 plants, if exposed to high CO2 levels for sufficient time will start to lose the initial benefits they gained from the excess CO2-because they reduce the amount of enzyme that processes the CO2 (as production of enzyme is an energy dependent process). This of course means that the Rubisco pathway will just become saturated sooner-bringing the plant back to its "default" growth rate. Also, BP's post ignores the damage to plant growth caused by heat stress, accelerated aging, & damage from flooding & drought-all of which are proving to be the side-effects of increased CO2 emissions.

Response: [Daniel Bailey] The comment Marcus refers to is
by Berényi Péter and is located here.

I'm so bored of this nonsense, have you actually ever grown anything BP or are you an armchair horticulturalist?

Extra CO2 works in e.g. grow houses, green houses, and sealed tunnels because the plants are in a protected environment with little Fred from the potting shed cuddling them 24/7

Put them outside of that environment where they are no longer isolated from other environmental influences, such as rainfall, sunlight and insects and all hell breaks loose.

http://www.sciencedaily.com/releases/2008/03/080324173612.htm

http://www.sciencedaily.com/releases/2006/04/060412204831.htm

Personally I'm an amateur who knows jack poop about horticulture after 10+ years of trying, I might even get the hang of it in another 30+ years if I lucky and assuming we have a functional environment...

One thing I have learned from all this is that if you mess around with the balance of these systems they can and they will kick back very, very hard and in ways you never ever thought about...

I'm going to talk about semantics for a moment, so if you are only interested in the science, then skip over this…

I think it is important to understand why someone might object to the term pollutant. The argument might go like this:

1) I am more likely to rely on a dictionary to get my definitions, rather than US legislation or the Encyclopedia Britannica.

2) I am in Australia, so I would usually refer to the Macquarie Dictionary as the authoritative source. Their definition for pollute is:

1. to make foul or unclean; dirty.
2. to make morally unclean; defile.
3. to render ceremonially impure; desecrate.

3) These senses of the word have connotations that don't really make sense in the case of CO2 as a greenhouse gase.

4) Thus the use of the word pollutant could appear to be imprecise and/or an attempt to use the fallacy of "loaded language" in order to persuade.

For many, this might seem like hairsplitting to distract from more substantive issues. However, I object when I see contrarians using language that I consider imprecise or loaded, so I think it fair to listen when they make the same charge.

I'd suggest that if we can make the case without describing CO2 as a pollutant, then it is probably worth doing so (both as a courtesy, and also to avoid getting diverted into a semantic debate). If we do use the word pollutant, then we should preface this by an explanation of where our definition is coming from.

davidh#18: "connotations that don't really make sense in the case of CO2 as a greenhouse gase."

You make an elegant argument; however, if you view CO2 as a waste product of fossil fuel consumption, the unregulated dumping of said waste into the open air would seem to fit your #1 definition of the verb 'pollute.'

davidh @18, regardless of the dictionary definition, "pollution" is not used that way in common language.

To take one example, I come from Mount Isa, whose copper ore has a high sulfur content. Consequently the emissions from the smelter had a high sulfur dioxide content, those emissions being traceable as far as the African coast. When the wind was in the right quarter, and weak enough, the sulfur dioxide would be carried into the town with the result that the sulfur dioxide formed into a weak acid when brought into contact with water, as in on the lining of the oesophagus and lungs. For many people that made breathing very difficult, and anything more than very light activity outside a significant health risk. If it rained, the acid was washed down onto plants, killing rose bushes across the town. What it did not do is make anything foul, unclean or dirty. I doubt that anyone would hesitate to call the SO2 pollution.

Also from Mount Isa, lead has been periodically released into the environment by a variety of means. Soil containing the lead was indistinguishable from soil not containing the lead other than by chemical analysis. But again, when high levels of lead contamination was found at a local kindergarten, no letters (I am sure) where sent to the paper saying it was not lead pollution because it did not make the soil "foul or unclean, or dirty".

One final example, also from the mines, in which ventilation was a major issue. One reason for that was to prevent the build up of carbon monoxide, which is famously a colourless, odourless gas, and hence by definition not foul, unclean or dirty. It also kills, so again I doubt anyone would hesitate to call it pollution.

More fundamentally, the important definition in this case is not the Macquarie Dictionary definition, but the legal definition. So, whether you go with New South Wales and say an act of polluting is:

"an offence of waste disposal if committed without lawful authority, wilfully or
negligently, in a manner that harms or is likely to harm the environment (s. 5)"

or with Victoria, and define it as:

"where a person intentionally, recklessly, or negligently pollutes the
environment or causes or permits an environmental hazard which results in:
· a serious threat to the environment;
· a serious threat to public health;
· a substantial risk of serious damage to the environment;
· a substantial risk of a serious threat to public health."

CO2 is a pollutant. That it is a waste product can hardly be argued, and that it poses a significant threat to the survival of the Great Barrier Reef, and hence "a substantial risk of serious damage to the environment" is well established.

The insistence that we not use perfectly accurate descriptive words because deniers don't like the connotations is Orwellian in a quite literal sense. It is an attempt to make thinking about the issue difficult by controlling the language used to do so.

(Firstly, let me make it clear that you don't need to convince me of the case for AGW and the likely risks we are facing because of it. My interest is in finding the best (least confronting and least confusing) way of communicating the issue to people who genuinely want to know, and who have to somehow wade through all the sound and fury out there to make a decision about what to believe.)

muoncounter#19: I take your point, but still think it is a bit of a stretch. I think you are using waste in the sense of "anything left over or superfluous, as excess material, by-products, etc., not of use for the work in hand". This doesn't lead easily to "foul", "unclean", or "dirty". This gets even more problematic when you have to reconcile industrial emissions with natural emissions (e.g. "Am I polluting by breathing?").

Tom Curtis#20: Personally, I largely agree with your assessment of the commonly understood meaning of pollution. I have used the term carbon pollution myself, but have moved away from it myself because of the resistance that I have encountered (which I think has some justification).

The places where I think your rebuttal needs to be strengthened are:

1) The assumption that everyone has the same (non-dictionary) understanding of "pollution".

2) The assumption that people will go to look at legislation (rather than a dictionary) when trying to resolve differences in opinion about the meaning of a word.

Part of the problem might be that we are concerned about different audiences - I am mainly concerned with members of the general public that are trying to make sense of this stuff (rather than scientists, lawyers, or legislators).

A secondary objection is that even if we accepted the legal definitions you propose, then I don't believe that carbon emissions fall under them (yet). Can you currently be prosecuted for polluting by emitting CO2? If not, I would have thought that CO2 emissions were (by definition) not pollution according to current law. I'm not a legal expert, so feel free to correct me if I'm wrong.

With regard to accusation of being Orwellian: I understand where you are coming from, but I don't think the accusation is quite justified (it would be doubleplusungood if it was ;-). I wasn't trying to _insist_ that we not use the word. I was trying to suggest that there might be reasons to look for alternatives, or at least be clear about where our definition was coming from when we do use it.

In summary, my own view is that while the use of the word pollution to refer to excess greenhouse gas emissions may become widely accepted in future, using this terminology at this point in time risks being counterproductive (depending on who you are talking to). But your mileage may vary…

my view may be jaundiced from so commonly encountering on the web so many genuine deniers. However, I suspect that only genuine deniers will in fact be troubled by the word "pollution". This is because of the obviously specious argumentative company it keeps, such as, for instance the claim that CO2 obviously is not a pollutant because we exhale it. Of course, we excrete other things but are quick to call it pollution when it washes up on Manly Beach, and everybody knows it. That style of argument is an appeal to thoughtlessness - an attempt to divert attention from a serious issue by a glib meme which is superficially attractive but can stand no scrutiny. Of course there is the more robust argument that CO2 cannot be pollution because it is plant food and ... Oh that's right, we excrete plant food out the other end as well and are still very happy to call it pollution if it is dumped untreated into a river or sea. So not so robust after all. There is even the argument that we put CO2 into soft drinks, but you really do not want to go into the use of urea as a dietary supplement.

The point is that the arguments commonly associated with the claim that CO2 is not a pollutant are all, and transparently specious. They would not be given serious consideration by any open minded person who actually thought about the issue. By not using the word pollution, we give those arguments rhetorical strength to substitute for their rational weakness.

If instead of doing that, we challenge the claim that CO2 is not a pollution, we can easily show that it is, by standard, common place definitions. Of course the deniers won't accept that, but they were never going to be convinced anyway. But people with an open mind will accept it, and think worse of the deniers and denialism for having used such specious arguments in the first place.

Having said that:

1) Actually I would be very surprised if more people used the "dictionary" definition then used the more practical definition enshrined in legislation. But of course, it may depend on which dictionary definition you use:

"pollution
The contamination of air, water, or soil by substances that are harmful to living organisms. Pollution can occur naturally, for example through volcanic eruptions, or as the result of human activities, such as the spilling of oil or disposal of industrial waste. Light from cities and towns at night that interferes with astronomical observations is known as light pollution. It can also disturb natural rhythms of growth in plants and other organisms. Continuous noise that is loud enough to be annoying or physically harmful is known as noise pollution. Heat from hot water that is discharged from a factory into a river or lake, where it can kill or endanger aquatic life, is known as thermal pollution.

If light and heat can be considered pollution, and no one misunderstands or disputes those descriptions, the CO2 certainly can be.

2) The assumption isn't that people will know or look at the legislative definitions. The assumption is that when they are pointed out, open minded people will recognize the objection to the use of the word "pollution" is specious.

davidh, you are using a definition of "pollute" to dispute the accuracy of calling CO2 "pollution".

They have the same root, but they are different words with different connotations. Look up the definitions of pollution or 'pollutant' in that "Macquarie Dictionary" you call authoritative and I guarantee you will find one which so describes anything which damages the environment.

I doubt there is a single major dictionary, encyclopedia, or 'environmental protection' type law anywhere which does not define "pollution" in such a way that it would include CO2.

davidh#21: "gets even more problematic when you have to reconcile industrial emissions with natural emissions (e.g. "Am I polluting by breathing?")."

That's just silly; we inhale much of the same CO2 we exhale. See the prior thread on breathing (use search). On the other hand, consumption of fossil fuels produces a waste product; on human time scales, it's a one-way process.

pollution
1. the act of polluting.
2. environmental pollutants, such as motor vehicle emissions, industrial waste, etc.
3. the results of these pollutants, as city smog, etc.

pollutant
that which pollutes; a polluting agent.

pollute
1. to make foul or unclean; dirty.
2. to make morally unclean; defile.
3. to render ceremonially impure; desecrate.

Using the second definition of "pollution", we can get CO2 as industrial waste (in the sense of "anything left over or superfluous, as excess material, by-products, etc."), and therefore as an environmental pollutant. (Interestingly, this particular definition doesn't seem to include damage to the environment as a consideration).

And so you are correct. I was largely persuaded by Tom Curtis and muoncounter, but this puts the icing on it by applying a more rigorous application of the authority I have proposed, without having to shift to other definitions.

Thanks to you all for your contributions to this. I will now feel a little more relaxed about using the term in future (though I will still use it with care).

Finally, one last appeal for patience and empathy: I realise the tremendous frustration at the poor quality of much of the discourse around this issue, but I do believe that there are many out there who genuinely hold different views or who genuinely don't know what to think. We need to make it as easy as possible for them to hear what we are saying... Thanks again all!

I think the question hangs on whether you believe global warming is on net harmful at the levels predicted. If you don't believe that the net effects of a 2 degree temperature rise are harmful then it's hard to get to the point of calling CO2 a pollutant. While there have been many dire predictions based on the 2 degree theory I have yet to see a well reasoned quantification of the relative benefits versus harms. Where can I find that?

I need a link to EPA's listing of CO2 as an air pollutant. This blog states "...the US Environmental Protection Agency (EPA) Administrator must publish a list of certain air pollutants....Greenhouse gases including CO2 unquestionably fit the Clean Air Act's broad definition of air pollutants and must be listed and regulated by the EPA if it can be determined that they endanger public heath and/or welfare." However, I cannot find an EPA list of air pollutants that includes CO2, and the links in this blog don't help. They lead to an EPA Endangerment Finding but not a statement that CO2 is an air pollutant. Or is that the same thing? I appreciate it.

CO2 is poisoness to animals and (especially) marine life at low concentrations. Past mass extinctions have been caused by high CO2 levels. Calling anything that causes mass extinctions a fertilizer is ludicrous.